What is the Mediterranean diet?

In the daily barrage of conflicting health advice, one theme stands out - eat a Mediterranean diet, and you will live a longer, healthier life. The latest addition to a list that includes reductions in childhood asthma, hay fever, and Alzheimer's is a 12-year study from the US which claims that eating the Mediterranean way can halve the risk of serious lung disease.

But 21 different countries border the Mediterranean - so where exactly is this fabled diet to be found? Greece? Italy? Lebanon? Minoan Crete? Paul Gayler, executive chef at the Lanesborough Hotel in London and author of the book Mediterranean Cook, declines to be specific. If he had to choose one typical country with a typical diet? "I suppose Italy." Then he qualifies it. "Spain and Italy. Or southern France."

"It's a lighter type of eating, isn't it," he says. "More things are grilled rather than fried." He goes on to cite vegetables, especially tomatoes, "low in fat" tuna and swordfish and, of course, olive oil (there is even a study which claims that taking four teaspoons a day can defend against cancer).

Not everyone is persuaded. "One thing they never tell you about the Mediterranean diet," says Matthew Fort, author of Eating Up Italy: Voyages on a Vespa, "is that in southern Italy, southern Spain and Sicily the fat used in cooking is pig fat and in North Africa it's mutton fat. Our understanding of the Mediterranean diet bears little resemblance to the diet of real people."

Fort argues that poverty has kept many reliant on vegetables, pulses, and cheap fish. Now there is more money, there is more meat, more fat, more obesity. It seems the "Mediterranean diet" is just a convenient shorthand for an ideal.